Aqueous solution

An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be represented as . The word aqueous (which comes from aqua) means pertaining to, related to, similar to, or dissolved in, water. As water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent in chemistry. Since water is frequently used as the solvent in experiments, the word solution refers to an aqueous solution, unless the solvent is specified. A non-aqueous solution is a solution in which the solvent is a liquid, but is not water. (See also Solvent and Inorganic nonaqueous solvent.) Substances that are hydrophobic ('water-fearing') do not dissolve well in water, whereas those that are hydrophilic ('water-friendly') do. An example of a hydrophilic substance is sodium chloride. In an aqueous solution the hydrogen ions () and hydroxide ions () are in Arrhenius balance ( = Kw = 1 x 10−14 at 298 K). Acids and bases are aqueous solutions, as part of their Arrhenius definitions. An example of an Arrhenius acid is hydrogen chloride (HCl) because of its dissociation of the hydrogen ion when dissolved in water. Sodium hydroxide (NaOH) is an Arrhenius base because it dissociates the hydroxide ion when it is dissolved in water. Aqueous solutions may contain, especially in the alkaline zone or subjected to radiolysis, hydrated atomic hydrogen and hydrated electrons. Aqueous solutions that conduct electric current efficiently contain strong electrolytes, while ones that conduct poorly are considered to have weak electrolytes. Those strong electrolytes are substances that are completely ionized in water, whereas the weak electrolytes exhibit only a small degree of ionization in water. The ability for ions to move freely through the solvent is a characteristic of an aqueous strong electrolyte solution. The solutes in a weak electrolyte solution are present as ions, but only in a small amount.